Vertical recording medium with thin soft magnetic film

ABSTRACT

A vertical magnetic recording medium includes a soft magnetic film formed on a substrate, and a vertical magnetization film formed on the soft magnetic film. μ·δb≧1000, when μ is a permeability of the soft magnetic film, and δb [nm] is a film thickness of the soft magnetic film. The permeability μ of the soft magnetic film is 5≦μ≦200, and the film thickness δb of the soft magnetic film is equal to or less than 500 nm. Also, vertical magnetic anisotropy energy Ku [erg/cc] of the vertical magnetization film is 1×10 7 ≦Ku≦7×10 8 , and coercive force Hc [kOe] of the vertical magnetization film in the vertical direction to a surface of the vertical magnetization film is 5≦Hc≦10.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vertical magnetic recording mediumsuitable for a magnetic disk.

2. Description of the Related Art

In recent years, a much larger capacity and a much smaller size havebeen required for had disk drives, as information devices such aspersonal computers and work stations have progressed. In magnetic disks,much higher density is also required.

However, in a longitudinal magnetic recording method which has beenbeing widely used, problems arise in that miniaturization of recordingbits incurs heat fluctuation in recording magnetization and that ahigher coercive force which may exceed the recording ability of arecording head is required, when realizing a high recording density.Hence, a vertical magnetic recording method has been discussed as amagnetic recording method capable of greatly improving the recordingdensity while solving the problems described above. As a kind ofvertical magnetic recording medium which realizes this method, there isa vertical magnetic recording medium having a two-layer structure whichis composed of a soft magnetic film with a high magnetic permeabilityand a vertical magnetization film with a high vertical anisotropy.

FIG. 1 is a schematic cross sectional view showing an example of aconventional vertical magnetic recording medium. The vertical magneticrecording medium 21 is composed of a lower soft magnetic film 23 and avertical magnetization film 24 which are laminated in an order on asubstrate 22 made of non-magnetic material. For example, a NiFe film isused as the lower soft magnetic film 23, and CoCr-based alloy is usedfor the vertical magnetization film 24 (Nippon-Ouyou-Jiki-Gakkai-Shi,Vol. 8, No. 1, 1984, pp. 17-22).

This vertical magnetic recording medium 21 achieves recording moreeasily than a conventional longitudinal magnetic recording methodbecause of existence of the lower soft magnetic film 23. That is, thisvertical magnetic recording medium 21 can easily perform recording sinceit has much greater vertical magnetic anisotropic energy than themagnetic anisotropic energy of a conventional longitudinal magneticrecording medium in the longitudinal direction and also has much greatercoercive force in the direction vertical to the film surface than aconventional longitudinal magnetic recording medium. Therefore, thevertical magnetic recording medium 21 can be stronger against heatfluctuation than a medium according to the longitudinal magneticrecording method. To deal with the problem of the heat fluctuation, ittends to use a film having high vertical magnetic anisotropic energy andcoercive force in the direction vertical to the film surface greaterthan those of a CoCr-based film which has been the main trend ofvertical magnetic films.

Meanwhile, in the conventional vertical magnetic recording medium usinga vertical magnetization film which has great vertical magneticanisotropic energy and large coercive force in the direction vertical tothe film surface, the magnetic permeability μ and film thickness δ_(b)of the lower soft magnetic film must be set to greater values in orderto maintain a recording sensitivity, than in the case of using aconventional vertical magnetization film.

Where a practical medium manufacturing process is considered, the lowersoft magnetic film should be thinner as much as possible. This isbecause a manufacturing process of the vertical magnetization filmformed on the lower soft magnetic film becomes easier. The verticalmagnetization film determines the recording/reproducing ability at ahigh recording density, when the lower soft magnetic film is thinned.

In conjunction with the above description, a vertical magnetic recordingmedium is disclosed in Japanese Laid Open Patent Application(JP-A-Heisei 4-283413). In this reference, a lower soft magnetic lininglayer (12) and a vertical magnetization film (13) are formed in order ona non-magnetic material substrate (11). After a magnetic polar surfacelayer of the lower soft magnetic layer (12) is removed by an ion etchingmethod or an inverse sputtering method, the vertical magnetization film(13) is formed thereon. The coercive force of the vertical magnetizationfilm (13) becomes gradually smaller into a direction of the phaseboundary with the lower soft magnetic layer (12) from the surface of thevertical magnetization film (13). Also, the saturation magnetizationbecomes gradually larger into a direction of the phase boundary with thelower soft magnetic layer (12) from the surface of the verticalmagnetization film (13).

Also, a vertical magnetic recording medium is disclosed in Japanese LaidOpen Patent Application (JP-A-Heisei 6-139542). In this reference, alower soft magnetic layer (12) and a vertical magnetization film (13)are formed in order on a non-magnetic material substrate (11). The lowersoft magnetic layer (12) has the relative permeability in a range of 20to 1000 and the saturation magnetic flux density of 10 kG or more.

Also, a vertical magnetic recording medium is disclosed in Japanese LaidOpen Patent Application (JP-A-Heisei 11-149628). In this reference, thevertical magnetic recording medium (20) is composed of a substrate (22),a lower soft magnetic film (24) formed on the substrate (22), and avertical magnetization film 28 formed on the lower soft magnetic film(24). The lower soft magnetic film (24) is provided not to have anon-magnetic wall structure. The coercive force of the lower softmagnetic film (24) is equal to or less than 300 Oe.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a vertical magneticrecording medium which can comply with thinning of the lower softmagnetic film.

Another object of the present invention is to provide a verticalmagnetic recording medium which has large vertical magnetic anisotropicenergy and large coercive force in the direction vertical to the filmsurface.

Still another object of the present invention is to provide a verticalmagnetic recording medium which can eliminate the problem of heatfluctuation.

In order to achieve an aspect of the present invention, a verticalmagnetic recording medium includes a soft magnetic film formed on asubstrate, and a vertical magnetization film formed on the soft magneticfilm, μ·δb≧1000, when μ is a permeability of the soft magnetic film, andδb [nm] is a film thickness of the soft magnetic film.

Here, it is desirable that the permeability μ of the soft magnetic filmis 5≦μ≦200. Also, it is desirable that the film thickness δb of the softmagnetic film is equal to or less than 500 nm.

Also, it is desirable that vertical magnetic anisotropy energy Ku[erg/cc] of the vertical magnetization film is 1×10⁷≦Ku≦7×10⁸. Also, itis desirable that coercive force Hc [kOe] of the vertical magnetizationfilm in the vertical direction to a surface of the verticalmagnetization film is 5≦Hc≦10.

Also, the vertical magnetization film may include FePt alloy. In thiscase, it is desirable that the vertical magnetization film comprises xat %Fe-(100-x) at %Pt alloy, where 40≦x≦60. It is more desirable thatthe vertical magnetization film comprises 50at %Fe-50at %Pt alloy, wherex=50 at %.

Also, the vertical magnetization film may include RCo alloy, where R isone or more selected from the group consisting of Y, Ce, Sm, La and Pr.In this case, the vertical magnetization film may include RCo₅ alloy,where R is one or more selected from the group consisting of Y, Ce andSm. Alternatively, the vertical magnetization film may include R₂Co₁₇alloy, where R is one or more selected from the group consisting of Y,Ce, Sm, La and Pr.

Also, the soft magnetic film may include FeSiAl alloy. In this case, itis desirable that the vertical magnetization film comprises 84.9wt%Fe-xwt %Si-(15.1-x)wt %Al alloy, where 8.0≦x≦12.0. It is more desirablethat the vertical magnetization film may include 84.9wt %Fe-9.6wt%Si-5.5wt %Al.

Also, the soft magnetic film may include CoNiFe alloy. Especially, it isdesirable that the soft magnetic film may include 62at %Co-12at %Ni-26at%Fe alloy.

In order to achieve another aspect of the present invention, a verticalmagnetic recording medium includes a soft magnetic film formed on asubstrate, and a vertical magnetization film formed on the soft magneticfilm, and μ·δb≧1000 when μ is a permeability of the soft magnetic film,and δb [nm] is a film thickness of the soft magnetic film. In addition,the permeability μ of the soft magnetic film is 5≦μ≦200, and the filmthickness δb of the soft magnetic film is equal to or less than 500 nm.

Here, it is desirable that the vertical magnetization film may includeFePt alloy or RCo alloy, where R is one or more selected from the groupconsisting of Y, Ce, Sm, La and Pr.

Also, it is desirable that the soft magnetic film may include FeSiAlalloy or CoNiFe alloy.

Also, it is desirable that vertical magnetic anisotropy energy Ku[erg/cc] of the vertical magnetization film is 1×10⁷≦Ku≦7×10⁸, andcoercive force Hc [kOe] of the vertical magnetization film in thevertical direction to a surface of the vertical magnetization film is5≦Hc≦10.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view showing an example of aconventional vertical magnetic recording medium;

FIG. 2 is a cross sectional view showing a vertical magnetic recordingmedium according to the present invention;

FIG. 3 is a cross sectional view showing a specific example of thevertical magnetic recording medium according to the present invention;and

FIG. 4 shows a relation of magnetic permeability μ of the lower softmagnetic film and the film thickness δ_(b) thereof in a region wherereproduce output is secured.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a vertical magnetic recording medium according to thepresent invention will now be described below in detail with referenceto the attached drawings.

FIG. 2 is a cross sectional view showing a vertical magnetic recordingmedium according to the present invention. The vertical magneticrecording medium 1 is composed of a lower soft magnetic film 3 with amagnetic permeability μ and a film thickness δ_(b), and a verticalmagnetization film 4 which are laminated on a substrate 2 made ofnon-magnetic material.

It is preferable that the magnetic permeability μ of the lower softmagnetic film 3 satisfies 5≦μ≦200, and the film thickness δ_(b) thereofis 500 nm or less. For example, alloys such as FeSiAl alloy and CoNiFealloy are used for the lower soft magnetic film 3. It is preferable thatas the FeSiAl alloy is used is 84.9wt %Fe-Xwt %Si-(15.1-X)wt %Al alloy(hereinafter, to be referred to as Fe_(84.9)-Si_(X)—Al_(15.1-X) alloy)where 8.0≦X≦12.0 is satisfied, for example. More preferably, thecomposition of the FeSiAl alloy is 84.9wt %Fe-9.6wt %Si-5.4wt %Al. Also,it is preferable that 62at %Co-12at %Ni-26at %Fe is used as the CoNiFealloy, for example.

It is preferable that the vertical magnetization film 4 has the verticalmagnetic anisotropic energy Ku [erg/cc] in a range of 1×10⁷≦Ku≦7×10⁸,and the coercive force Hc [kOe] in the direction vertical to its filmsurface in a range of 5≦Hc≦10. For example, FePt alloy or RCo alloy(where R is one or more selected from the group consisting of Y, Ce, Sm,La, and Pr) is used for the vertical magnetization film 4. It ispreferable that as the FePt alloy is used X at %Fe-(100-X)at %Pt alloy(hereinafter, to be referred to as Fe_(x)-Pt_(100-x)) where 40≦X≦60 issatisfied, for example. It is more preferable that composition of theFePt alloy is 50at %Fe-50at %Pt. Also, it is preferable that as the Rcoalloy is Rco₅ alloy (where R is one or more selected from the groupconsisting of Y, Ce, and Sm), R₂Co₁₇ alloy (where R is one or moreselected from the group consisting of Y, Ce, Sm, La, and Pr). In thevertical magnetic recording medium 1, a condition of μ·δ_(b)≧1000 issatisfied where the magnetic permeability of the lower soft magneticfilm 3 is μ and the thickness thereof is δ_(b) [nm]. Therefore,sufficient reproduction sensitivity can be maintained even if the lowersoft magnetic film 3 is thinned.

FIG. 3 is a cross sectional view showing a specific example of avertical magnetic recording medium according to the first embodiment.The vertical magnetic recording medium 11 is composed of a 84.9wt%Fe-9.6wt %Si-5.5wt %Al film 13 (hereinafter to be referred to as aFe_(84.9)Si_(9.6)Al_(5.5) film 13) as a lower soft magnetic film with amagnetic permeability μ and a film thickness δ_(b), and a 50at %Fe-50at%Pt film 14 (hereinafter to be referred to as a Fe₅₀Pt₅₀ film 14) as avertical magnetization film 4, which are laminated on a substrate 2 madeof non-magnetic material.

Next, a vertical magnetic recording medium according to the presentinvention will be described more specifically.

The First Embodiment

Samples were formed to have Fe_(84.9)Si_(9.6)Al_(5.5) films 13 whichwere formed on substrates 12 of a 2.5-inch size at the substratetemperature of 400° C. by a sputtering method by use of 84.9wt %Fe-9.6wt%Si-5.5wt %Al targets of a 6-inch size. The samples had ten differentthicknesses of 2, 5, 10, 20, 50, 100, 200, 250, 500, and 750 nm. Thefilm forming condition was set in such a manner that the suppliedelectric power was 0.5 kw, the argon gas pressure was 4 mTorr (5.31×10⁻¹Pa), and the film forming rate was 3 nm/sec at the initial vacuum degreeof 5×10⁻⁷ mTorr (6.65×10⁻⁸ Pa) to 7 mTorr (9.31×10⁻¹ Pa).

The ten types of samples were heated with a lamp in a sputter chamber.The heating time was changed so as to prepare the ten samples withFe_(84.9)Si_(9.6)Al_(5.5) films 13 having different magneticpermeabilities μ. The magnetic permeabilities μ were changed in a rangeof seven types of 2, 5, 10, 20, 50, 100, and 200. In other words,mediums respectively having seven types of magnetic permeabilities μwere prepared for each of ten types of different film thicknesses δ_(b).Thus, total seventy different types mediums withFe_(84.9)Si_(9.6)Al_(5.5) films 13 were prepared. The mediums with theFe_(84.9)Si_(9.6)Al_(5.5) films 13 having combinations of a permeabilityμ and a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ,δb)=(5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5)were respectively named vertical magnetic recording mediums A1 to A6 inthe first embodiment.

Also, Fe₅₀Pt₅₀ films 14 were respectively formed onFe_(84.9)Si_(9.6)Al_(5.5) films 13 by 50 nm at the substrate temperatureof 450° C. by use of a target of 50at %Fe-50at %Pt, for the purpose ofmeasurement of magnetic permeabilities. Further, a C protection film wasformed by 5 nm on each of the Fe₅₀Pt₅₀ films 14.

Also, as comparison examples, mediums with Fe_(84.9)Si_(9.6)Al_(5.5)films 13 having combinations of a permeability μ and a film thicknessδ_(b) [nm] that satisfy μ·δ_(b)=500, e.g., (μ, δ_(b))=(5, 100), (10,50), (50, 10), and (100, 5) were respectively named comparative mediumsAA1 to AA4. In addition, a medium with Fe_(84.9)Si_(9.6)Al_(5.5) films13 having combinations of a permeability μ and a film thickness δ_(b)[nm] that satisfy μ·δ_(b)=400, e.g., (μ, δ_(b))=(20, 20) was named acomparison medium AA5. Further, mediums with Fe_(84.9)Si_(9.6)Al_(5.5)films 13 having combinations of permeabilities μ=2 to 200 and a filmthickness δb=750 nm were respectively named comparison mediums AA6 toAA12.

Further, samples were formed on substrates of a 12-inch size at thesubstrate temperature of 400° C. by a sputtering method by use of 21.5wt%Ni-78.5wt %Fe target of a 6-inch size, to have five differentthicknesses of 5, 10, 50, 100, and 200 nm. The film forming conditionwas set in such a manner that the supplied electric power was 0.5 KW,the argon gas pressure was 4 mTorr (5.31×10⁻¹ Pa), and the film formingspeed was 3 nm/sec, at the initial vacuum degree of 5×10⁻⁷ mTorr(6.65×10⁻⁸ Pa) to 7 mTorr (9.31×10⁻¹ Pa). The samples with theNi_(21.5)Fe_(78.5) films having different film thicknesses were heatedwith a lamp in a sputter chamber. The heating time was changed so as toprepare Ni_(21.5)Fe_(78.5) films having different magneticpermeabilities μ. The magnetic permeabilities μ were changed in a rangeof seven kinds of 2, 5, 10, 20, 50, 100, and 200. In other words,mediums with the Ni_(21.5)Fe_(78.5) films respectively having sevenmagnetic permeabilities μ were prepared for every one of five differentfilm thicknesses δ_(b). Thus, total thirty-five different kinds ofsamples with Ni_(21.5)Fe_(78.5) films were prepared.

Samples with Fe₅₀Pt₅₀ films were respectively formed on theNi_(21.5)Fe_(78.5) films by 50 nm by use of 50at %Fe-50at %Pt targetsfor the purpose of measurement of magnetic permeability. Further, a Cprotection film was formed by 5 nm on each of the samples. At this time,mediums with the Ni_(21.5)Fe_(78.5) films having combinations of apermeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and(200, 10) were respectively named conventional mediums AB1 to AB4. Inaddition, mediums with the Ni_(21.5)Fe_(78.5) films having combinationsof a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=1000, e.g., (μ, δb)=(5, 200), (10, 100), (20, 50), (50, 20),(100, 10), and (200, 5) were respectively named conventional comparisonmediums AC1 to AC6. It should be noted that the Ni_(21.5)Fe_(78.5) filmwas generally used for a lower soft magnetic film conventionally.

Then, the vertical magnetic anisotropic energy Ku of each Fe₅₀Pt₅₀ filmwas measured by a magnetic torque meter to find Ku=7×10⁷ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=5.5 [kOe].

Recording/reproducing tests were carried out to total seventy kinds ofvertical magnetic recording mediums having seven kinds of permeabilitiesfor each of ten different film thicknesses of Fe_(84.9)Si_(9.6)Al_(5.5)films 13, by use of a monopolar head and a MR head respectively used asa recording head and a reproducing head. The MR head had a reproductiontrack width of 1 μm and a reproduction gap length of 0.1 μm. Themonopolar head has a track width of 1.5 μm. Evaluations were carried outunder the condition that the recording current was 10 mAop, the sensecurrent was 12 mA, the circumferential speed was 12.7 m/s, and thefloating amount was 45 nm. A signal having a recording density of 300kFRPI was recorded, and thereafter, a reproduced output thereof wasmeasured.

Table 1 shows reproduced outputs (μV) of the seventy kinds of sampleswith Fe_(84.9)Si_(9.6)Al_(5.5) films 13. This table shows the mediumsaccording to the first embodiment and the mediums of comparison examplesclearly separated.

TABLE 1 Reproduced output

*values of comparison mediums in solid line block *values of mediums inthe first embodiment in dotted line block

As can be seen from the table 1, the reproduced outputs weresufficiently secured in the region lower than the mediums A1 to A6 inthe first embodiment, (i.e., in the region of the present embodiment).On the other hand, reproduced outputs can be greatly lowered in theregion upper than the comparison mediums AA6 to AA12, (i.e., in theregion of the conventional samples).

FIG. 4 shows the results obtained above in a different manner, where thehorizontal axis expresses the magnetic permeability μ of the lower softmagnetic film and the vertical axis expresses the film thickness δ_(b)thereof. As seen from this FIG. 4, sufficient reproduced outputs can besecured where μ·δ_(b)≧1000 was satisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is 2, sufficient reproduced outputs cannot be secured with respectto any of the film thicknesses δ_(b). Also, in case where the filmthickness δ_(b) is 2 nm, sufficient reproduced outputs cannot be securedwith respect to any of the permeabilities μ. This is because thepermeability μ and film thickness δ_(b) of the lower soft magnetic filmare lower than required. Further, the reproduced output tends todecrease even when the film thickness δ_(b) of the lower soft magneticfilm exceeds 500 nm. This is because the surface smoothness of the lowersoft magnetic film was disturbed since the film thickness δ_(b) of thelower soft magnetic film is thicker than required. Consequently, thevertical orientation of the vertical magnetization film formed on thelower soft magnetic film is deteriorated. Hence, it is found that allvalues of (μ, δ_(b)) that satisfy the relationship of μ·δ_(b)≧1000cannot be always used for practical design, even if the relationship ofμ·δ_(b)≦1000 is satisfied. It is necessary to satisfy the relationshipof μ·δ_(b)≧1000 and simultaneously to satisfy a relationship of 5≦μ≦200and a relationship that δ_(b) is 500 nm or less.

Similarly, a signal having a recording density of 300 kFRPI was recordedon the conventional mediums AB1 to AB4 and the conventional comparisonmediums AC1 to AC6. Reproduced outputs were thereafter measured with aMR head. The measurement values were shown in Table 2.

TABLE 2 Reproduced output Conventional Conventional ConventionalConventional Medium Medium Medium Medium AB1 AB2 AB3 AB4 460 522 516 503Conven- Conven- Conven- Conven- Conven- Conven- tional tional tionaltional tional tional compari compari compari compari compari compari sonson son son son son medium medium medium medium medium medium AC1 AC2AC3 AC4 AC5 AC6 192 142 152 165 174 187 Unit: μV

As can be seen from the Table 2, the value of μ·δ_(b)=1000 isinsufficient to obtain securely a recording/reproducing sensitivity andthe value of μ·δ_(b) requires at least μ·δ_(b)=2000 or more, in case ofa vertical magnetic recording medium which uses a Ni_(21.5)Fe_(78.5)film as the lower soft magnetic film. From the above, a verticalmagnetic recording medium having a Fe_(84.9)Si_(9.6)Al_(5.5) film as itslower soft magnetic film can obtain more securely arecording/reproducing sensitivity than a vertical magnetic recordingmedium having a Ni_(21.5)Fe_(78.5) film as its lower soft magnetic film,even if the value of μ·δ_(b) is smaller. As a result of this, the lowersoft magnetic film can be designed to be thinner. This is because theFe_(84.9)Si_(9.6)Al_(5.5) film has smaller anisotropy and is moreisotropic than the Ni_(21.5)Fe_(78.5) film. Therefore, theFe_(84.9)Si_(9.6)Al_(5.5) film has a higher sensitivity to the magneticfield generated by the recording head, so that the recording/reproducingsensitivity is improved as a result.

From the above, if a Fe_(84.9)Si_(9.6)Al_(5.5) film is used in place ofa Ni_(21.5)Fe_(78.5) film for a vertical magnetic recording medium,design can be made with a lower value of μ·δ_(b). If the relationship ofμ·δ_(b)≧1000 is satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500nm are satisfied simultaneously where the magnetic permeability of theFe_(84.9)Si_(9.6)Al_(5.5) film is μ and the film thickness thereof isμ_(b), the recording/reproducing sensitivity can be sufficientlyobtained even in case where the vertical magnetic anisotropic energy Kuand the coercive force Hc in the direction vertical to the film surfaceare much greater than those of conventional vertical magnetizationfilms, as in the first embodiment. As a result, by using aFe_(84.9)Si_(9.6)Al_(5.5) film as a lower soft magnetic film and bysatisfying the conditions of μ·δ_(b)≧1000, 5 ≦μ≦200, and δ_(b)≦500 nm,the lower soft magnetic film can be more thinned than the case of usinga Ni_(21.5)Fe_(78.5) film which is often used conventionally as a lowersoft magnetic film, even if where the vertical magnetic anisotropicenergy Ku and the coercive force Hc in the direction vertical to thefilm surface are much greater than those of conventional CoCr-basedvertical magnetization films (e.g., Ku is about 5×10⁶ [erg/cc] and Hc isabout 3 [kOe]), as in the case of the material used in the firstembodiment.

The Second Embodiment

Like the first embodiment, total seventy different kinds of samples withFe84.9Si_(9.6)Al_(5.5) films were prepared by use of 84.9wt %Fe-9.6wt%Si-5.5wt %Al targets, i.e., Fe_(84.9)Si_(9.6)Al_(5.5) filmsrespectively having seven different magnetic permeabilities μ wereprepared for every one of ten different film thicknesses δ_(b). Also,like the first embodiment, mediums were prepared by use of 40at %Fe-60at%Pt targets in place of the 50at %Fe-50at %Pt targets in the firstembodiment, on Fe_(84.9)Si_(9.6)Al_(5.5) films formed separately fromthose formed for the purpose of measurement of magnetic permeability.

At this time, like the first embodiment, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ,δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5)were respectively named vertical magnetic recording mediums B1 to B6according to the second embodiment. In addition, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=500, e.g., (μ,δ_(b))=(5, 100), (10, 50), (50, 10), and (100, 5) were respectivelynamed comparison mediums BB1 to BB4. Also, a medium havingFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfies μ·δ_(b)=400, e.g., (μ,δ_(b))=(20, 20) was named a comparison medium BB5. Further, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films each having permeabilities μ=2 to 200and a film thickness δ_(b)=750 nm were respectively named comparisonmediums BB6 to BB12.

Also, in the second embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) films as the lower soft magnetic film were formed tohave a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δb=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and (200,10). Also, conventional comparison mediums AC1 to AC6 havingNi_(21.5)Fe_(78.5) films as the lower soft magnetic film were formed tohave a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20),(100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Fe₄₀Pt₆₀ filmwas measured by a magnetic torque meter to find Ku=1×10⁸ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=7.0 [kOe].

Recording/reproducing tests were carried out to total seventy kinds ofvertical magnetic recording mediums having seven differentpermeabilities for every one of ten different film thicknesses of lowersoft magnetic films, under the same conditions as those of the firstembodiment. Specifically, a signal having a recording density of 300kFRPI was recorded, and thereafter, a reproduced output thereof wasmeasured. Table 3 shows the values of reproduced outputs. This table 3also shows which values belong to which of the mediums according to thesecond embodiment and the comparison mediums.

TABLE 3 reproduced output

*values of comparison mediums in solid line block *values of mediums inthe second embodiment in dotted line block

As can be seen from the table 3, the reproduced outputs are sufficientlysecured in the region lower than the mediums B1 to B6 in the secondembodiment. On the other hand, reproduced outputs can be greatly loweredin the region upper than the comparison mediums BB6 to BB12. FIG. 4 alsosummarizes the results obtained above, in a different manner, where thehorizontal axis expresses the magnetic permeability μ of the lower softmagnetic film and the vertical axis expresses the film thickness δ_(b)thereof. As seen from this FIG. 4, sufficient reproduced outputs can besecured where μ·δ_(b)≧1000 is satisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is two, sufficient reproduced outputs cannot be secured withrespect to any of the film thicknesses δ_(b). Also, in case where thefilm thickness δ_(b) is 2 nm, sufficient reproduced outputs cannot besecured with respect to any of the permeabilities μ. This is because thepermeability μ and the film thickness δ_(b) are lower than required.Further, the reproduced output tends to decrease even when the filmthickness δ_(b) of the lower soft magnetic film exceeds 500 nm. This isbecause the surface smoothness of the lower soft magnetic film isdisturbed since the film thickness δ_(b) of the lower soft magnetic filmis thicker than required. Consequently, the vertical orientation of thevertical magnetization film formed on the lower soft magnetic film isdeteriorated. Hence, it is found that all values of (μ, δ_(b)) thatsatisfy the relationship of μ·δ_(b)≧1000 cannot be always used forpractical design even if the relationship of μ·δ_(b)≧1000 is satisfied.It is necessary to satisfy the relationship of μ·δ_(b)≧1000 andsimultaneously to satisfy a relationship of 5≦μ≦200 and a relationshipthat δ_(b) is 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI isrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs are thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, it could be understood that a vertical two-layer mediumwhich uses a Fe_(84.9)Si_(9.6)Al_(5.5) film as its lower soft magneticfilm can obtain more securely a recording/reproducing sensitivity than avertical two-layer medium which uses a Ni_(21.5)Fe_(78.5) film as itslower soft magnetic film, even if the value of μ·δ_(b) is small. Inother words, the lower soft magnetic film can be designed to be thinner.This is because the Fe_(84.9)Si_(9.6)Al_(5.5) film has smalleranisotropy and is more isotropic than the Ni_(21.5)Fe_(78.5) film.Therefore, the Fe_(84.9)Si_(9.6)Al_(5.5) film has a higher sensitivityto the magnetic field generated by the recording head, so that therecording/reproducing sensitivity is improved as a result.

From the above, if a Fe_(84.9)Si_(9.6)Al_(5.5) film is used in place ofa Ni_(21.5)Fe_(78.5) film for a vertical two-layer medium, design can bemade with a lower value of μ·δ_(b). If the relationship of μ·δ_(b)≧1000is satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500 nm aresatisfied simultaneously where the magnetic permeability of theFe_(84.9)Si_(9.6)Al_(5.5) film is μ and the film thickness thereof isδ_(b), sufficient recording/reproducing sensitivity can be secured evenin case where the vertical magnetic anisotropic energy Ku and thecoercive force Hc in the direction vertical to the film surface are muchgreater than those of conventional vertical magnetization films, as inthe second embodiment. As a conclusion, by using aFe_(84.9)Si_(9.6)Al_(5.5) film as a lower soft magnetic film and bysatisfying the conditions of μ·δ_(b)≧1000, 5≦μ≦200, and δ_(b)≦500 nm,the lower soft magnetic film can be made thinner than in the case ofusing a Ni_(21.5)Fe_(78.5) film which is often used conventionally as alower soft magnetic film, even if where the vertical magneticanisotropic energy Ku and the coercive force Hc in the directionvertical to the film surface are much greater than those of conventionalCoCr-based vertical magnetization films (e.g., Ku is about 5×10⁶[erg/cc] and Hc is about 3 [kOe]), as in the case of the material usedin the second embodiment. Accordingly, it is possible to obtain a novelvertical two-layer medium in which the lower soft magnetic film is madethin and a process of manufacturing a medium is made easier.

The Third Embodiment

Like the first embodiment, total seventy different kinds of samples withFe_(84.9)Si_(9.6)Al_(5.5) films were prepared by use of 84.9wt %Fe-9.6wt%Si-5.5wt %Al targets, i.e., Fe_(84.9)Si_(9.6)Al_(5.5) filmsrespectively having seven different magnetic permeabilities μ wereprepared for every one of ten different film thicknesses δ_(b). Also,like the first embodiment, mediums were prepared using 60at %Fe-40at %Pttargets in place of the 50at %Fe-50at %Pt targets in the firstembodiment, on Fe_(84.9)Si_(9.6)Al_(5.5) films formed separately fromthose formed for the purpose of magnetic permeability measurement.

At this time, like the first embodiment, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ,δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5)were respectively named vertical magnetic recording mediums C1 to C6according to the third embodiment. In addition, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δb=500, e.g., (μ,δ_(b))=(5, 100), (10, 50), (50, 10), and (100, 5) were respectivelynamed comparison mediums CC1 to CC4. Also, a medium havingFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfies μ·δ_(b)=400, e.g., (μ,δ_(b))=(20, 20) was named a comparison medium CC5. Further, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films each having permeabilities μ=2 to 200and a film thickness δ_(b)=750 nm were respectively named comparisonmediums CC6 to CC12.

Also, in the second embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) films as the lower soft magnetic film were formed tohave a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δb=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and (200,10). Also, conventional comparison mediums AC1 to AC6 as verticaltwo-layer mediums having Ni_(21.5)Fe_(78.5) films as the lower softmagnetic film were formed to have a permeability μ and a film thicknessδ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10,100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Fe₆₀Pt₄₀ filmwas measured by a magnetic torque meter to find Ku=5×10⁷ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=5.0 [kOe].

Recording/reproducing tests were made to total seventy kinds of verticalmagnetic recording mediums having seven different permeabilities forevery one of ten different film thicknesses of lower soft magneticfilms, under the same conditions as those of the first embodiment.Specifically, a signal having a recording density of 300 kFRPI wasrecorded, and thereafter, a reproduced output thereof was measured.Table 4 shows the values of reproduced outputs. This table 4 also showswhich values belong to which of the mediums according to the thirdembodiment and the comparison mediums.

TABLE 4 Reproduced output

*values of comparison mediums in solid line block *values of mediums inthe third embodiment in dotted line block

As can be seen from the table 4, the reproduced outputs weresufficiently secured in the region lower than the mediums C1 to C6 inthe third embodiment. On the other hand, reproduced outputs can begreatly lowered in the region upper than the comparison mediums CC6 toCC12. FIG. 4 also summarizes the results obtained above, in a differentmanner, where the horizontal axis expresses the magnetic permeability μof the lower soft magnetic film and the vertical axis expresses the filmthickness δ_(b) thereof. From this FIG. 4, it is found that sufficientreproduced outputs can be secured where μ·δ_(b)≧1000 is satisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is two, sufficient reproduced outputs cannot be secured withrespect to any of the film thicknesses δ_(b). Also, in case where thefilm thickness δ_(b) is 2 nm, sufficient reproduced outputs cannot besecured with respect to any of the permeabilities μ. This is because thepermeability μ and the film thickness δ_(b) of the lower soft magneticfilm were lower than required. Further, the reproduced output tends todecrease even when the film thickness δ_(b) of the lower soft magneticfilm exceeds 500 nm. This is because the surface smoothness of the lowersoft magnetic film is disturbed since the film thickness δ_(b) of thelower soft magnetic film is thicker than required. Consequently, thevertical orientation of the vertical magnetization film formed thereonis deteriorated. Hence, it is found that all values of (μ, δ_(b)) thatsatisfy the relationship of μ·δ_(b)≧1000 cannot be always used forpractical design even if the relationship of μ·δ_(b)≧1000 is satisfied.But, it is necessary to satisfy the relationship of μ·δ_(b)≧1000 and tosatisfy simultaneously a relationship of 5≦μ≦200 and a relationship thatδ_(b) was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI wasrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs are thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, a vertical two-layer medium which uses aFe_(84.9)Si_(9.6)Al_(5.5) film as its lower soft magnetic film canobtain more securely a recording/reproducing sensitivity than a verticaltwo-layer medium which uses a Ni_(21.5)Fe_(78.5) film as its lower softmagnetic film, even if the value of μ·δ_(b) is small. In other words,the lower soft magnetic film can be designed to be thinner. This isbecause the Fe_(84.9)Si_(9.6)Al_(5.5) film has smaller anisotropy and ismore isotropic than the Ni_(21.5)Fe_(78.5) film. Therefore, theFe_(84.9)Si_(9.6)Al_(5.5) film has a higher sensitivity to the magneticfield generated by the recording head, so that the recording/reproducingsensitivity is improved as a result.

From the above, if a Fe_(84.9)Si_(9.6)Al_(5.5) film is used in place ofa Ni_(21.5)Fe_(78.5) film for a vertical two-layer medium, design can bemade with a lower value of μ·δ_(b). If the relationship of μ·δ_(b)≧1000was satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500 nm aresimultaneously satisfied where the magnetic permeability of theFe_(84.9)Si_(9.6)Al_(5.5) film is μ and the film thickness thereof isδ_(b), a sufficient recording/reproducing sensitivity can be securedeven in case where the vertical magnetic anisotropic energy Ku and thecoercive force Hc in the direction vertical to the film surface are muchgreater than those of conventional vertical magnetization films, as inthe present embodiment. As a result, by using aFe_(84.9)Si_(9.6)Al_(5.5) film as a lower soft magnetic film and bysatisfying the conditions of μ·δ_(b)≧1000, 5≦μ≦200, and δ_(b)≦500 nm,the lower soft magnetic film can be made thinner than in the case ofusing a Ni_(21.5)Fe_(78.5) film which is often used conventionally as alower soft magnetic film, even if where the vertical magneticanisotropic energy Ku and the coercive force Hc in the directionvertical to the film surface are much greater than those of conventionalCoCr-based vertical magnetization films (e.g., Ku is about 5×10⁶[erg/cc] and Hc is about 3 [kOe]), as in the case of the material usedin the present embodiment. Accordingly, it is possible to obtain a novelvertical two-layer medium in which the lower soft magnetic film can bemade thin and a process of manufacturing a medium can be made easier.

It should be noted that since similar advantages were obtained by usingrespectively Fe₄₀Pt₆₀ films in the second embodiment, Fe₅₀Pt₅₀ films inthe first embodiment, and Fe₆₀Pt₄₀ films in the third embodiment asvertical magnetization films, it is apparent that the vertical magneticanisotropic energy is distributed within a range of 5×10⁷[erg/cc]≦Ku≦1×10⁸ [erg/cc] and the coercive force in the directionvertical to the film surface is distributed within a range of 5[kOe]≦Hc≦7 [kOe] as long as a Fe_(X)Pt_(100-X) film has X which falls inthe range of 40≦X≦60 in X at %Fe-(100-X)at %Pt. Hence, it was alsoapparent that similar advantages can be obtained as long as aFe_(X)Pt_(100-X) film has X which falls in the range of 40≦X≦60 in X at%Fe-(100-X)at %Pt.

The Fourth Embodiment

In the same manner as in the first embodiment, Fe_(84.9)Si_(8.0)Al_(7.1)films were formed on substrates using 84.9wt %Fe-8.0wt %Si-7.1wt %Altargets in place of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets used in thefirst embodiment. Like the first embodiment, total seventy differentkinds of Fe_(84.9)Si_(8.0)Al_(7.1) films were prepared to have sevendifferent magnetic permeabilities μ for every one of ten different filmthicknesses δ_(b). Also, like the first embodiment, mediums wereprepared using YCo₅ (at %) targets in place of the 50at %Fe-50at %Pttargets used in the first embodiment, on Fe_(84.9)Si_(8.0)Al_(7.1) filmsformed separately from those formed for the purpose of measurement ofmagnetic permeability.

At this time, like the first embodiment, mediums withFe_(84.9)Si_(8.0)Al_(7.1) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ,δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5)were respectively named vertical magnetic recording mediums D1 to D6according to the fourth embodiment. In addition, mediums withFe_(84.9)Si_(8.0)Al_(7.1) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=500, e.g., (μ,δ_(b))=(5, 100), (10, 50), (50, 10), and (100, 5) were respectivelynamed comparison mediums DD1 to DD4. Also, a medium havingFe_(84.9)Si_(8.0)Al_(7.1) films each having a permeability μ and a filmthickness δ_(b) [nm] that satisfies μ·δ_(b)=400, e.g., (μ, δ_(b))=(20,20) was named a comparison medium DD5. Further, mediums withFe_(84.9)Si_(8.0)Al_(7.1) films each having permeabilities μ=2 to 200and a film thickness δ_(b)=750 nm were respectively named comparisonmediums DD6 to DD12.

Also, in the fourth embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) films as the lower soft magnetic films were formed tohave a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and(200, 10). Also, conventional comparison mediums AC1 to AC6 as verticaltwo-layer mediums having Ni_(21.5)Fe_(78.5) films as the lower softmagnetic film were formed to have a permeability μ and a film thicknessδ_(b) [nm] satisfy μ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10, 100),(20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each YCO₅ film wasmeasured by a magnetic torque meter to find Ku=1×10⁷ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=6.5 [kOe].

Recording/reproducing tests were carried out to total seventy kinds ofvertical magnetic recording mediums having seven differentpermeabilities for every one of ten different film thicknesses of lowersoft magnetic films, under the same conditions as those of the firstembodiment. Specifically, a signal having a recording density of 300kFRPI was recorded, and thereafter, a reproduced output thereof wasmeasured. Table 5 shows the values of reproduced outputs. This table 5also shows which values belong to which of the mediums according to thepresent embodiment and the comparison mediums.

TABLE 5 Reproduced output

*values of comparison mediums in solid line block *values of mediums inthe third embodiment in dotted line block

As can be seen from the table 5, the reproduced outputs weresufficiently secured in the region lower than the mediums D1 to D6 ofthe present embodiment. On the other hand, reproduced outputs can begreatly lowered in the region upper than the comparison mediums DD6 toDD12. FIG. 4 also summarizes the results obtained above, in a differentmanner, where the horizontal axis expresses the magnetic permeability μof the lower soft magnetic film and the vertical axis expresses the filmthickness δ_(b) thereof. From this FIG. 4, it is found that sufficientreproduced outputs can be secured where μ·δ_(b)≧1000 is satisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is two, sufficient reproduced outputs cannot be secured withrespect to any of the film thicknesses δ_(b). In case where the filmthickness δ_(b) is 2 nm, sufficient reproduced outputs cannot be securedwith respect to any of the permeabilities μ. This is because thepermeability μ and the film thickness δ_(b) were lower than required.Further, the reproduced output tends to decrease even when the filmthickness δ_(b) of the lower soft magnetic film exceeds 500 nm. This isbecause the surface smoothness of the lower soft magnetic film isdisturbed since the film thickness δ_(b) of the lower soft magnetic filmis thicker than required. Consequently, the vertical orientation of thevertical magnetization film formed thereon is deteriorated. Hence, it isfound that all values of (μ, δ_(b)) that satisfy the relationship ofμ·δ_(b≧1000) cannot be always used for practical design even if therelationship of μ·δ_(b)≧1000 was satisfied. It is necessary to satisfythe relationship of μ·δ_(b)≧1000 and simultaneously to satisfy arelationship of 5≦μ≦200 and a relationship that δ_(b) was 500 nm orless.

On the other hand, a signal having a recording density of 300 kFRPI isrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs are thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, a vertical two-layer medium which uses aFe_(84.9)Si_(8.0)Al_(7.1) film as its lower soft magnetic film canobtain more securely a recording/reproducing sensitivity than a verticaltwo-layer medium which uses a Ni_(21.5)Fe_(78.5) film as its lower softmagnetic film, even if the value of μ·δ_(b) is small. In other words,the lower soft magnetic film can be designed to be thinner. This isbecause the Fe_(84.9)Si_(8.0)Al_(7.1) film has smaller anisotropy and ismore isotropic than the Ni_(21.5)Fe_(78.5) film. Therefore, theFe_(84.9)Si_(8.0)Al_(7.1) film has a higher sensitivity to the magneticfield generated by the recording head, so that the recording/reproducingsensitivity is improved as a result.

From the above, if a Fe_(84.9)Si_(8.0)Al_(7.1) film was used in place ofa Ni_(21.5)Fe_(78.5) film for a vertical two-layer medium, design can bemade with a lower value of μ·δ_(b). If the relationship of μ·δ_(b)≧1000is satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500 nm aresatisfied simultaneously where the magnetic permeability of theFe_(84.9)Si_(8.0)Al_(7.1) film is μ and the film thickness thereof isμ_(b), sufficient recording/reproducing sensitivity can be secured evenin case where the vertical magnetic anisotropic energy Ku and thecoercive force Hc in the direction vertical to the film surface are muchgreater than those of conventional vertical magnetization films, as inthe fourth embodiment. As a conclusion, by using aFe_(84.9)Si_(8.0)Al_(7.1) film as a lower soft magnetic film and bysatisfying the conditions of μ·δ_(b)≧1000, 5≦μ≦200, and δ_(b)≦500 nm,the lower soft magnetic film can be made thinner than in the case ofusing a Ni_(21.5)Fe_(78.5) film which is often used conventionally as alower soft magnetic film, even if where the vertical magneticanisotropic energy Ku and the coercive force Hc in the directionvertical to the film surface are much greater than those of conventionalCoCr-based vertical magnetization films (e.g., Ku is about 5×10⁶[erg/cc] and Hc is about 3 [kOe]), as in the case of the material usedin the fourth embodiment. Accordingly, it is possible to obtain a novelvertical two-layer medium in which the lower soft magnetic film can bemade thin and process of manufacturing a medium can be made easier.

The Fifth Embodiment

In the same manner as in the first embodiment,Fe_(84.9)Si_(12.0)Al_(3.1) films were formed on substrates using 84.9wt%Fe-12.0wt %Si-3.1wt %Al targets in place of 84.9wt %Fe-9.6wt %Si-5.5wt%Al targets used in the first embodiment. Like the first embodiment,total seventy different kinds of Fe_(84.9)Si_(12.0)Al_(3.1) films wereprepared to have seven different magnetic permeabilities μ for every oneof ten different film thicknesses δ_(b). Also, like the firstembodiment, mediums were prepared using CeCo₅ (at %) targets in place ofthe 50at %Fe-50at %Pt targets used in the first embodiment, onFe_(84.9)Si_(12.0)Al_(3.1) films formed separately from those formed forthe purpose of magnetic permeability measurement.

At this time, like the first embodiment, mediums withFe_(84.9)Si_(12.0)Al_(3.1) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ,δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5)were respectively named vertical magnetic recording mediums E1 to E6according to the fifth embodiment. In addition, mediums withFe_(84.9)Si_(12.0)Al_(3.1) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=500, e.g., (μ,δ_(b))=(5, 100), (10, 50), (50, 10), and (100, 5) were respectivelynamed comparison mediums EE1 to EE4. Also, a medium havingFe_(84.9)Si12.0Al_(3.1) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfies μ·δ_(b)=400, e.g., (μ,δ_(b))=(20, 20) was named a comparison medium EE5. Further, mediumshaving permeabilities μ=2 to 200 and a film thickness δ_(b)=750 nm wererespectively named comparison mediums EE6 to EE12.

Also, in the fifth embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) as the lower soft magnetic films which were formed tohave a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and(200, 10). Also, conventional comparison mediums AC1 to AC6 as verticaltwo-layer mediums having Ni_(21.5)Fe_(78.5) films as the lower softmagnetic film were formed to have a permeability μ and a film thicknessδ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10,100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each CeCo₅ film wasmeasured by a magnetic torque meter to find Ku=5.5×10⁷ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=6.5 [kOe].

Recording/reproducing tests were made to total seventy kinds of verticalmagnetic recording mediums having seven different permeabilities forevery one of ten different film thicknesses of lower soft magneticfilms, under the same conditions as those of the first embodiment.Specifically, a signal having a recording density of 300 kFRPI wasrecorded, and thereafter, a reproduced output thereof was measured.Table 6 shows the values of reproduced outputs. This table 6 also showswhich values belong to which of the mediums according to the presentembodiment and the comparison mediums.

TABLE 6 Reproduced outputs

*values of comparison mediums in solid line block *values of mediums inthe fourth embodiment in dotted line block

As can be seen from the table 6, the reproduced outputs weresufficiently secured in the region lower than the mediums E1 to E6 ofthe present embodiment. On the other hand, reproduced outputs can begreatly lowered in the region upper than the comparison mediums EE6 toEE12. FIG. 4 also summarizes the results obtained above, in a differentmanner, where the horizontal axis expresses the magnetic permeability μof the lower soft magnetic film and the vertical axis expresses the filmthickness δ_(b) thereof. From FIG. 4, it is found that sufficientreproduced outputs can be secured where μ·δ_(b)≧1000 is satisfied.

Also, in case where the magnetic permeability μ of the lower softmagnetic film is two, sufficient reproduced outputs cannot be securedwith respect to any of the film thicknesses δ_(b), Also, in case wherethe film thickness δ_(b) is 2 nm, sufficient reproduced outputs cannotbe secured with respect to any of the permeabilities μ. This is becausethe permeability μ and the film thickness δ_(b) were lower thanrequired. Further, the reproduced output tends to decrease even when thefilm thickness δ_(b) of the lower soft magnetic film exceeds 500 nm.This is because the surface smoothness of the lower soft magnetic filmis disturbed since the film thickness δ_(b) of the lower soft magneticfilm is thicker than required. Consequently, the vertical orientation ofthe vertical magnetization film formed on the lower soft magnetic filmis deteriorated. Hence, it is found that all values of (μ, δ_(b)) thatsatisfy the relationship of μ·δ_(b)≧1000 cannot be always used forpractical design even if the relationship of μ·δ_(b)≧1000 was satisfied.It is necessary to satisfy the relationship of μ·δ_(b)≧1000 and tosatisfy simultaneously a relationship of 5≦μ≦200 and a relationship thatδ_(b) was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI isrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs were thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, a vertical two-layer medium which uses aFe_(84.9)Si_(12.0)Al_(3.1) film as its lower soft magnetic film canobtain more securely a recording/reproducing sensitivity than a verticaltwo-layer medium which uses a Ni_(21.5)Fe_(78.5) film as its lower softmagnetic film, even if the value of μ·δ_(b) is small. In other words,the lower soft magnetic film can be designed to be thinner. This isbecause the Fe_(84.9)Si_(12.0)Al_(3.1) film has smaller anisotropy andis more isotropic than the Ni_(21.5)Fe_(78.5) film. Therefore, theFe_(84.9)Si_(12.0)Al_(3.1) film has a higher sensitivity to the magneticfield generated by the recording head, so that the recording/reproducingsensitivity is improved as a result.

From the above, if a Fe_(84.9)Si_(12.0)Al_(3.1) film was used in placeof a Ni_(21.5)Fe_(78.5) film for a vertical two-layer medium, design canbe made with a lower value of μ·δ_(b). If the relationship ofμ·δ_(b)≧1000 was satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500nm were satisfied simultaneously where the magnetic permeability of theFe_(84.9)Si_(12.0)Al_(3.1) film is μ and the film thickness thereof isδ_(b), sufficient recording/reproducing sensitivity can be secured evenin case where the vertical magnetic anisotropic energy Ku and thecoercive force Hc in the direction vertical to the film surface are muchgreater than those of conventional vertical magnetization films, as inthe present embodiment. As a conclusion, by using aFe_(84.9)Si_(12.0)Al_(3.1) film as a lower soft magnetic film and bysatisfying the conditions of ν·δ_(b)≧1000, 5≦μ≦200, and δ_(b)≦500 nm,the lower soft magnetic film can be more thinned than in the case ofusing a Ni_(21.5)Fe_(78.5) film which is often used conventionally as alower soft magnetic film, even if where the vertical magneticanisotropic energy Ku and the coercive force Hc in the directionvertical to the film surface are much greater than those of conventionalCoCr-based vertical magnetization films (e.g., Ku is about 5×10⁶[erg/cc] and Hc is about 3 [kOe]), as in the case of the material usedin the fifth embodiment. Accordingly, it is possible to obtain a novelvertical two-layer medium in which the lower soft magnetic film can bemade thinner and a process of manufacturing a medium can be made easier.

It should be noted that since similar advantages are obtained by usingrespectively Fe_(84.9)Si_(8.0)Al_(7.1) films in the fourth embodiment,Fe_(84.9)Si_(9.6)Al_(5.5) films in the first embodiment, andFe_(84.9)Si_(12.0)Al_(3.1) films in the fifth embodiment as verticalmagnetization films, it is apparent that similar advantages can beobtained as long as a Fe_(84.9)-Si_(X)-Al_(15.1-X) lower soft magneticfilm has X which falls in the range of 8.0≦X≦12.0 (wt %) inFe_(84.9)-Si_(X)-Al_(15.1-X).

The Sixth Embodiment

In the same manner as in the first embodiment, Co₆₂Ni₁₂Fe₂₆ films wereformed on substrates using 62wt %Co-12wt %Ni-26wt %Fe targets in placeof 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets used in the first embodiment.Like the first embodiment, total seventy different kinds of Co₆₂Ni₁₂Fe₂₆films were prepared to have seven different magnetic permeabilities μfor every one of ten different film thicknesses δ_(b). Also, like thefirst embodiment, mediums were prepared using SmCo₅ (at %) targets inplace of the 50at %Fe-50at %Pt targets used in the first embodiment, onCo₆₂Ni₁₂Fe₂₆ films formed separately from those formed for the purposeof magnetic permeability measurement.

At this time, like the first embodiment, mediums having Co₆₂Ni₁₂Fe₂₆films having combinations of a permeability μ and a film thickness δ_(b)[nm] that satisfy μ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10, 100),(20, 50), (50, 20), (100, 10), and (200, 5) were respectively namedvertical magnetic recording mediums F1 to F6 according to the presentembodiment. In addition, mediums having Co₆₂Ni₁₂Fe₂₆ films havingcombinations of a permeability μ and a film thickness δ_(b) [nm] thatsatisfy μ·δ_(b)=500, e.g., (μ, δ_(b))=(5, 100), (10, 50), (50, 10), and(100, 5) were respectively named comparison mediums FF1 to FF4. Also, amedium having Co₆₂Ni₁₂Fe₂₆ films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfies ν·δ_(b)=400, e.g., (ν,5b)=(20, 20) was named a comparison medium FF5. Further, mediums havingCo₆₂Ni₁₂Fe₂₆ films each having permeabilities μ=2 to 200 and a filmthickness δ_(b)=750 nm were respectively named comparison mediums FF6 toFF12.

Also, in the fifth embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) as the lower soft magnetic films were formed to havea permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and(200, 10). Also, conventional comparison mediums AC1 to AC6 as verticaltwo-layer mediums having Ni_(21.5)Fe_(78.5) films as the lower softmagnetic film were formed to have a permeability μ and a film thicknessδ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10,100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each SmCo₅ film wasmeasured by a magnetic torque meter to find Ku=1×10⁸ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=7.0 [kOe].

Recording/reproducing tests were made to total seventy kinds of verticalmagnetic recording mediums having seven different permeabilities forevery one of ten different film thicknesses of lower soft magneticfilms, under the same conditions as those of the first embodiment.Specifically, a signal having a recording density of 300 kFRPI wasrecorded, and thereafter, a reproduced output thereof was measured.Table 7 shows the values of reproduced outputs. This table 7 also showswhich values belong to which of the mediums according to the presentembodiment and the comparison mediums.

TABLE 7 Reproduced output

*values of comparison mediums in solid line block *values of mediums inthe sixth embodiment in dotted line block

As can be seen from the table 7, the reproduced outputs are sufficientlysecured in the region lower than the mediums F1 to F6 of the presentembodiment. On the other hand, reproduced outputs can be greatly loweredin the region upper than the comparison mediums FF6 to FF12. FIG. 4 alsosummarizes the results obtained above, in a different manner, where thehorizontal axis expresses the magnetic permeability μ of the lower softmagnetic film and the vertical axis expresses the film thickness δ_(b)thereof. From this FIG. 4, it is found that sufficient reproducedoutputs can be secured where μ·δ_(b)≧1000 is satisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is two, sufficient reproduced outputs cannot be secured withrespect to any of the film thicknesses δ_(b). In case where the filmthickness δ_(b) is 2 nm, sufficient reproduced outputs cannot be securedwith respect to any of the permeabilities μ. This is because thepermeability μ and the film thickness δ_(b) were lower than required.Further, the reproduced output tends to decrease even when the filmthickness δ_(b) of the lower soft magnetic film exceeds 500 nm. This isbecause the surface smoothness of the lower soft magnetic film isdisturbed since the film thickness δ_(b) of the lower soft magnetic filmis thicker than required. Consequently, the vertical orientation of thevertical magnetization film formed on the lower soft magnetic film isdeteriorated. Hence, it is found that all values of (μ, δ_(b)) thatsatisfy the relationship of μ·δ_(b)≧1000 cannot be always used forpractical design even if the relationship of ν·δ_(b)≧1000 is satisfied.It is necessary to satisfy the relationship of μ·δ_(b)≧1000 andsimultaneously to satisfy a relationship of 5≦μ≦200 and a relationshipthat δ_(b) was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI isrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs are thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, a vertical two-layer medium which uses a Co₆₂Ni₁₂Fe₂₆film as its lower soft magnetic film can obtain more securely arecording/reproducing sensitivity than a vertical two-layer medium whichuses a Ni_(21.5)Fe_(78.5) film as its lower soft magnetic film, even ifthe value of μ·δ_(b) is small. In other words, the lower soft magneticfilm can be designed to be thinner. This is because the Co₆₂Ni₁₂Fe₂₆film has greater saturation magnetization than the Ni_(21.5)Fe_(78.5)film. Therefore, the Co₆₂Ni₁₂Fe₂₆ film has a higher sensitivity to themagnetic field generated by the recording head, so that therecording/reproducing sensitivity is improved as a result.

From the above, if a Co₆₂Ni₁₂Fe₂₆ film is used in place of aNi_(21.5)Fe_(78.5) film for a vertical two-layer medium, design can bemade with a lower value of μ·δ_(b). If the relationship of μ·δ_(b)≧1000is satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500 nm aresatisfied simultaneously where the magnetic permeability of theCo₆₂Ni₁₂Fe₂₆ film is μ and the film thickness thereof is δ_(b),sufficient recording/reproducing sensitivity can be secured even in casewhere the vertical magnetic anisotropic energy Ku and the coercive forceHc in the direction vertical to the film surface are much greater thanthose of conventional vertical magnetization films, as in the sixthembodiment. As a conclusion, by using a Co₆₂Ni₁₂Fe₂₆ film as a lowersoft magnetic film and by satisfying the conditions of μ·δ_(b)≧1000,5≦μ≦200, and δ_(b)≦500 nm, the lower soft magnetic film can be madethinner than in the case of using a Ni_(21.5)Fe_(78.5) film which isoften used conventionally as a lower soft magnetic film, even if wherethe vertical magnetic anisotropic energy Ku and the coercive force Hc inthe direction vertical to the film surface are much greater than thoseof conventional CoCr-based vertical magnetization films (e.g., Ku isabout 5×10⁶ [erg/cc] and Hc is about 3 [kOe]), as in the case of thematerial used in the present embodiment. Accordingly, it is possible toobtain a novel vertical two-layer medium which enables thinning of thelower soft magnetic film and easier process of manufacturing a medium.

The Seventh Embodiment

Like the first embodiment, total seventy different kinds of sampleshaving Fe_(84.9)Si_(9.6)Al_(5.5) films were prepared by use of 84.9wt%Fe-9.6wt %Si-5.5wt %Al targets, i.e., Fe_(84.9)Si_(9.6)Al_(5.5) filmsrespectively having seven different magnetic permeabilities μ wereprepared for every one of ten different film thicknesses δ_(b). Also,like the first embodiment, mediums were prepared using Y₂Co₁₇ (at %)targets in place of the 50at %Fe-50at %Pt targets used in the firstembodiment, on Fe_(84.9)Si_(9.6)Al_(5.5) films formed separately fromthose formed for the purpose of measurement of magnetic permeability. Atthis time, like the first embodiment, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ,δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5)were respectively named vertical magnetic recording mediums G1 to G6according to the seventh embodiment. In addition, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=500, e.g., (μ,δ_(b))=(5, 100), (10, 50), (50, 10), and (100, 5) were respectivelynamed comparison mediums GG1 to GG4. Also, a medium havingFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfies μ·δ_(b)=400, e.g., (μ,δ_(b))=(20, 20) was named a comparison medium GG5. Further, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films each having permeabilities μ=2 to 200and a film thickness δ_(b)=750 nm were respectively named comparisonmediums GG6 to GG12.

Also, in the seventh embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) as the lower soft magnetic films were formed to havea permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and(200, 10). Also, conventional comparison mediums AC1 to AC6 as verticaltwo-layer mediums having Ni_(21.5)Fe_(78.5) films as the lower softmagnetic film were formed to have a permeability μ and a film thicknessδ_(b) [nm] that satisfy μ·δ_(b)=1000, e.g., (μ, δb)=(5, 200), (10, 100),(20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Y₂Co₁₇ filmwas measured by a magnetic torque meter to find Ku=2×10⁸ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=8.0 [kOe].

Recording/reproducing tests were made on total seventy kinds of verticalmagnetic recording mediums having seven different permeabilities forevery one of ten different film thicknesses of lower soft magneticfilms, under the same conditions as those of the first embodiment.Specifically, a signal having a recording density of 300 kFRPI wasrecorded, and thereafter, a reproduced output thereof was measured.Table 8 shows the values of reproduced outputs. This table 8 also showswhich values belong to which of the mediums according to the seventhembodiment and the comparison mediums.

TABLE 8 Reproduced outputs

*values of comparison mediums in solid line block *values of mediums inthe seventh embodiment in dotted line block

As can be seen from the table 8, the reproduced outputs are sufficientlysecured in the region lower than the mediums G1 to G6 of the presentembodiment. On the other hand, reproduced outputs can be greatly loweredin the region upper than the comparison mediums GG6 to GG12. FIG. 4 alsosummarizes the results obtained above, in a different manner, where thehorizontal axis expresses the magnetic permeability μ of the lower softmagnetic film and the vertical axis expresses the film thickness δ_(b)on the lower soft magnetic film. From this FIG. 4, it is found thatsufficient reproduced outputs can be secured where μ·δ_(b)≧1000 issatisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is two, sufficient reproduced outputs cannot be secured withrespect to any of the film thicknesses δ_(b). Also, in case where thefilm thickness δ_(b) is 2 nm, sufficient reproduced outputs cannot besecured with respect to any of the permeabilities μ. This is because thepermeability μ and the film thickness δ_(b) are lower than required.Further, the reproduced output tends to decrease even when the filmthickness δ_(b) of the lower soft magnetic film exceeds 500 nm. This isbecause the surface smoothness of the lower soft magnetic film isdisturbed since the film thickness δ_(b) of the lower soft magnetic filmis thicker than required. Consequently, the vertical orientation of thevertical magnetization film formed on the lower soft magnetic film isdeteriorated. Hence, it is found that all values of (μ, δ_(b)) thatsatisfy the relationship of μ·δ_(b)≧1000 cannot be always used forpractical design even if the relationship of μ·δ_(b)≧1000 is satisfied.It is necessary to satisfy the relationship of μ·δb≧1000 and to satisfysimultaneously a relationship of 5≦μ≦200 and a relationship that δ_(b)was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI isrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs are thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, a vertical two-layer medium which uses aFe84.9Si_(9.6)Al_(5.5) film as its lower soft magnetic film can obtainmore securely a recording/reproducing sensitivity than a verticaltwo-layer medium which uses a Ni_(21.5)Fe_(78.5) film as its lower softmagnetic film, even if the value of μ·δ_(b) is small. In other words,the lower soft magnetic film can be designed to be thinner. This isbecause the Fe_(84.9)Si_(9.6)Al_(5.5) film has smaller anisotropy and ismore isotropic than the Ni_(21.5)Fe_(78.5) film. Therefore, theFe_(84.9)Si_(9.6)Al_(5.5) film has a higher sensitivity to the magneticfield generated by the recording head, so that the recording/reproducingsensitivity is improved as a result.

From the above, if a Fe_(84.9)Si_(9.6)Al_(5.5) film was used in place ofa Ni_(21.5)Fe_(78.5) film for a vertical two-layer medium, design can bemade with a lower value of μ·δ_(b). If the relationship of μ·δ_(b)≧1000was satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500 nm aresatisfied simultaneously where the magnetic permeability of theFe_(84.9)Si_(9.6)Al_(5.5) film is μ and the film thickness thereof isδ_(b), a sufficient recording/reproducing sensitivity can be securedeven in case where the vertical magnetic anisotropic energy Ku and thecoercive force Hc in the direction vertical to the film surface are muchgreater than those of conventional vertical magnetization films, as inthe seventh embodiment. As a conclusion, by using aFe_(84.9)Si_(9.6)Al_(5.5) film as a lower soft magnetic film and bysatisfying the conditions of μ·δ_(b)≧1000, 5≦μ≦200, and δ_(b)≦500 nm,the lower soft magnetic film can be more thinned than in the case ofusing a Ni_(21.5)Fe_(78.5) film which is often used conventionally as alower soft magnetic film, even if where the vertical magneticanisotropic energy Ku and the coercive force Hc in the directionvertical to the film surface are much greater than those of conventionalCoCr-based vertical magnetization films (e.g., Ku is about 5×10⁶[erg/cc] and Hc is about 3 [kOe]), as in the case of the material usedin the present embodiment. Accordingly, it is possible to obtain a novelvertical two-layer medium in which the lower soft magnetic film can bemade thinner and a process of manufacturing a medium can be made easier.

The Eighth Embodiment

Like the first embodiment, total seventy different kinds ofFe_(84.9)Si_(9.6)Al_(5.5) films were prepared by use of 84.9wt %Fe-9.6wt%Si-5.5wt %Al targets, i.e., Fe_(84.9)Si_(9.6)Al_(5.5) filmsrespectively having seven different magnetic permeabilities μ wereprepared for every one of ten different film thicknesses δ_(b). Also,like the first embodiment, mediums were prepared using CeCo₁₇ (at %)targets in place of the 50at %Fe-50at %Pt targets used in the firstembodiment, on Fe_(84.9)Si_(9.6)Al_(5.5) films formed separately fromthose formed for the purpose of measurement of magnetic permeability.

At this time, like the first embodiment, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·_(b)=1000, e.g., (μ,δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5)were respectively named vertical magnetic recording mediums H1 to H6according to the present embodiment. In addition, mediums withFe_(84.9)Si_(9.6)Al_(5.5) films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfy μ·δ_(b)=500, e.g., (μ,δ_(b))=(5, 100), (10, 50), (50, 10), and (100, 5) were respectivelynamed comparison mediums HH1 to HH4. Also, a medium having a combinationwhich satisfies μ·δ_(b)=400, e.g., (μ, δ_(b)) =(20, 20) was named acomparison medium HH5. Further, mediums with Fe_(84.9)Si_(9.6)Al_(5.5)films each having permeabilities μ=2 to 200 and a film thicknessδ_(b)=750 nm were respectively named comparison mediums HH6 to HH12.

Also, in the eighth embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) as the lower soft magnetic films which were formed tohave a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and(200, 10). Also, conventional comparison mediums AC1 to AC6 as verticaltwo-layer mediums having Ni_(21.5)Fe_(78.5) as the lower soft magneticfilms were formed to have a permeability μ and a film thickness δ_(b)[nm] that satisfy μ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10, 100),(20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each CeCo₁₇ filmwas measured by a magnetic torque meter to find Ku=5×10⁸ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=8.5 [kOe].

Recording/reproducing tests were made on total seventy kinds of verticalmagnetic recording mediums having seven different permeabilities forevery one of ten different film thicknesses of lower soft magneticfilms, under the same conditions as those of the first embodiment.Specifically, a signal having a recording density of 300 kFRPI wasrecorded, and thereafter, a reproduced output thereof was measured.Table 9 shows the values of reproduced outputs. This table 9 also showswhich values belong to which of the mediums according to the presentembodiment and the comparison mediums.

TABLE 9 Reproduced Outputs

*values of comparison mediums in solid line block *values of mediums inthe eighth embodiment in dotted line block

As can be seen from the table 9, the reproduced outputs are sufficientlysecured in the region lower than the mediums H1 to H6 of the eighthembodiment. On the other hand, reproduced outputs can be greatly loweredin the region upper than the comparison mediums HH6 to HH12. FIG. 4 alsosummarizes the results obtained above, in a different manner, where thehorizontal axis expresses the magnetic permeability μ of the lower softmagnetic film and the vertical axis expresses the film thickness δ_(b)thereof. From this FIG. 4, it is found that sufficient reproducedoutputs can be secured where μ·δ_(b)≧1000 is satisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is two, sufficient reproduced outputs cannot be secured withrespect to any of the film thicknesses δ_(b). In case where the filmthickness δ_(b) is 2 nm, sufficient reproduced outputs cannot be securedwith respect to any of the permeabilities μ. This is because thepermeability μ and the film thickness δ_(b) are lower than required.Further, the reproduced output tends to decrease even when the filmthickness δ_(b) of the lower soft magnetic film exceeds 500 nm. This isbecause the surface smoothness of the lower soft magnetic film isdisturbed since the film thickness δ_(b) of the lower soft magnetic filmis thicker than required. Consequently, the vertical orientation of thevertical magnetization film formed on the lower soft magnetic film isdeteriorated. Hence, it is found that all values of (μ, δ_(b)) thatsatisfy the relationship of μ·δ_(b)≧1000 cannot be always used forpractical design even if the relationship of a μ·δ_(b)≧1000 wassatisfied. It is necessary to satisfy the relationship of ν·δ_(b)≧1000and to satisfy simultaneously a relationship of 5≦μ≦200 and arelationship that δ_(b) was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI wasrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs were thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, a vertical two-layer medium which uses aFe_(84.9)Si_(9.6)Al_(5.5) film as its lower soft magnetic film canobtain more securely a recording/reproducing sensitivity than a verticaltwo-layer medium which uses a Ni_(21.5)Fe_(78.5) film as its lower softmagnetic film, even if the value of μ·δ_(b) is small. In other words,the lower soft magnetic film can be designed to be thinner. This isbecause the Fe_(84.9)Si_(9.6)Al_(5.5) film has smaller anisotropy and ismore isotropic than the Ni_(21.5)Fe_(78.5) film. Therefore, theFe_(84.9)Si_(9.6)Al_(5.5) film has a higher sensitivity to the magneticfield generated by the recording head, so that the recording/reproducingsensitivity is improved as a result.

From the above, if a Fe_(84.9)Si_(9.6)Al_(5.5) film was used in place ofa Ni_(21.5)Fe_(78.5) film for a vertical two-layer medium, design can bemade with a lower value of μ·δ_(b). If the relationship of a δ_(b)≧1000is satisfied and if relationships of 5≦μ≦200 and δ_(b)≦500 nm aresatisfied simultaneously where the magnetic permeability of theFe_(84.9)Si_(9.6)Al_(5.5) film was μ and the film thickness thereof wasμ_(b), sufficient recording/reproducing sensitivity can be secured evenin case where the vertical magnetic anisotropic energy Ku and thecoercive force Hc in the direction vertical to the film surface are muchgreater than those of conventional vertical magnetization films, as inthe eight embodiment. As a conclusion, by using aFe_(84.9)Si_(9.6)Al_(5.5) film as a lower soft magnetic film and bysatisfying the conditions of ν·δ_(b)≧1000, 5≧μ≧200, and δ_(b)≦500 nm,the lower soft magnetic film can be made thinner than in the case ofusing a Ni_(21.5)Fe_(78.5) film which is often used conventionally as alower soft magnetic film, even if where the vertical magneticanisotropic energy Ku and the coercive force Hc in the directionvertical to the film surface are much greater than those of conventionalCoCr-based vertical magnetization films (e.g., Ku is about 5×10⁶[erg/cc] and Hc is about 3 [kOe]), as in the case of the material usedin the present embodiment. Accordingly, it is possible to obtain a novelvertical two-layer medium in which the lower soft magnetic film can bemade thinner and a process of manufacturing a medium can be made easier.

The Ninth Embodiment

In the same manner as in the first embodiment, samples were prepared inwhich Co₆₂Ni₁₂Fe₂₆ films were formed on substrates using 62wt %Co-12wt%Ni-26wt %Fe targets were used in place of 84.9wt %Fe-9.6wt %Si-5.5wt%Al targets used in the first embodiment. Like the first embodiment,total seventy different kinds of samples with Co₆₂Ni₁₂Fe₂₆ films wereprepared. Also, like the first embodiment, mediums were prepared usingSmCo₁₇ (at %) targets in place of the 50at %Fe-50at %Pt targets used inthe first embodiment, on Co₆₂Ni₁₂Fe₂₆ films formed separately from thoseformed for the purpose of measurement of magnetic permeability.

At this time, like the first embodiment, mediums having Co₆₂Ni₁₂Fe₂₆films having combinations of a permeability μ and a film thickness δ_(b)[nm] that satisfy μ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10, 100),(20, 50), (50, 20), (100, 10), and (200, 5) were respectively namedvertical magnetic recording mediums J1 to J6 according to the ninthembodiment. In addition, mediums having Co₆₂Ni₁₂Fe₂₆ films havingcombinations of a permeability μ and a film thickness δ_(b) [nm] thatsatisfy μ·δ_(b)=500, e.g., (μ, δ_(b))=(5, 100), (10, 50), (50, 10), and(100, 5) were respectively named comparison mediums JJ1 to JJ4. Also, amedium having Co₆₂Ni₁₂Fe₂₆ films having combinations of a permeability μand a film thickness δ_(b) [nm] that satisfies μ·δ_(b)=400, e.g., (μ,δ_(b))=(20, 20) was named a comparison medium JJ5. Further, mediumshaving Co₆₂Ni₁₂Fe₂₆ films each having permeabilities μ=2 to 200 and afilm thickness δ_(b)=750 nm were respectively named comparison mediumsJJ6 to JJ12.

Also, in the ninth embodiment, like the first embodiment, conventionalmediums AB1 to AB4 as vertical two-layer mediums havingNi_(21.5)Fe_(78.5) films as the lower soft magnetic films were formed tohave a permeability μ and a film thickness δ_(b) [nm] that satisfyμ·δ_(b)=2000, e.g., (μ, δ_(b))=(10, 200), (20, 100), (100, 20), and(200, 10). Also, conventional comparison mediums AC1 to AC6 were formedto have a permeability μ and a film thickness δ_(b) [nm] satisfyμ·δ_(b)=1000, e.g., (μ, δ_(b))=(5, 200), (10, 100), (20, 50), (50, 20),(100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Sm₂Co₁₇ filmwas measured by a magnetic torque meter to find Ku=7×10⁸ [erg/cc]. Inaddition, the coercive force in the direction vertical to the filmsurface was measured by a Kerr rotation angle measurement device to findHc=10.0 [kOe].

Recording/reproducing tests were made to total seventy kinds of verticalmagnetic recording mediums having seven different permeabilities forevery one of ten different film thicknesses of lower soft magneticfilms, under the same conditions as those of the first embodiment.Specifically, a signal having a recording density of 300 kFRPI wasrecorded, and thereafter, a reproduced output thereof was measured.Table 10 shows the values of reproduced outputs. This table 10 alsoshows which values belong to which of the mediums according to the ninthembodiment and the comparison mediums.

TABLE 10 Reproduced outputs

*values of comparison mediums in solid line block *values of mediums inthe ninth embodiment in dotted line block

As can be seen from the table 10, the reproduced outputs aresufficiently secured in the region lower than the mediums J1 to J6 ofthe present embodiment. On the other hand, reproduced outputs can begreatly lowered in the region upper than the comparison mediums JJ6 toJJ12. FIG. 4 also summarizes the results obtained above, in a differentmanner, where the horizontal axis expresses the magnetic permeability μof the lower soft magnetic film and the vertical expresses the filmthickness δ_(b) thereof. From FIG. 4, it is found that sufficientreproduced outputs can be secured where μ·δ_(b)≧1000 is satisfied.

In case where the magnetic permeability μ of the lower soft magneticfilm is two, sufficient reproduced outputs cannot be secured withrespect to any of the film thicknesses δ_(b). In case where the filmthickness δ_(b) is 2 nm, sufficient reproduced outputs cannot be securedwith respect to any of the permeabilities μ. This is because thepermeability μ and the film thickness δ_(b) were lower than required.Further, the reproduced output tends to decrease even when the filmthickness δ_(b) of the lower soft magnetic film exceeds 500 nm. This isbecause the surface smoothness of the lower soft magnetic film isdisturbed since the film thickness δ_(b) of the lower soft magnetic filmis thicker than required. Consequently, the vertical orientation of thevertical magnetization film formed thereon is deteriorated. Hence, it isfound that all values of (μ, δ_(b)) that satisfy the relationship ofμ·δ_(b)≧1000 cannot be always used for practical design even if therelationship of μ·δ_(b)≧1000 is satisfied. But, it is necessary tosatisfy the relationship of μ·δ_(b)≧1000 and to satisfy simultaneously arelationship of 5≦μ≦200 and a relationship that δ_(b) was 500 nm orless.

On the other hand, a signal having a recording density of 300 kFRPI wasrecorded on the conventional mediums AB1 to AB4 and the conventionalcomparison mediums AC1 to AC6. Reproduced outputs were thereaftermeasured with a MR head. As shown in the first embodiment, the value ofμ·δ_(b)=1000 is insufficient to obtain securely a recording/reproducingsensitivity but the value of μ·δ_(b) requires at least μ·δ_(b)=2000 ormore. From this, a vertical two-layer medium which uses a Co₆₂Ni₁₂Fe₂₆film as its lower soft magnetic film can obtain more securely arecording/reproducing sensitivity than a vertical two-layer medium whichuses a Ni_(21.5)Fe_(78.5) film as its lower soft magnetic film, even ifthe value of μ·δ_(b) is small. In other words, the lower soft magneticfilm can be designed to be thinner. This is because the Co₆₂Ni₁₂Fe₂₆film has greater saturation magnetization than the Ni_(21.5)Fe_(78.5)film. Therefore, the Co₆₂Ni₁₂Fe₂₆ film has a higher sensitivity to themagnetic field generated by the recording head, so that therecording/reproducing sensitivity is improved as a result.

From the above, if a Co₆₂Ni₁₂Fe₂₆ film was used in place of aNi_(21.5)Fe_(78.5) film for a vertical two-layer medium, design can bemade with a lower value of μ·δ_(b). If the relationship of μ·δ_(b)≧1000is satisfied and if relationships of 5≦ν≦200 and δ_(b)≦500 nm aresatisfied simultaneously where the magnetic permeability of theCo₆₂Ni₁₂Fe₂₆ film is μ and the film thickness thereof is δ_(b),sufficient recording/reproducing sensitivity can be secured even in casewhere the vertical magnetic anisotropic energy Ku and the coercive forceHc in the direction vertical to the film surface are much greater thanthose of conventional vertical magnetization films, as in the presentembodiment. As a conclusion, by using a Co₆₂Ni₁₂Fe₂₆ film as a lowersoft magnetic film and by satisfying the conditions of μ·δ_(b)≧1000,5≦μ≦200, and δ_(b)≦500 nm, the lower soft magnetic film can be morethinned than in the case of using a Ni_(21.5)Fe_(78.5) film which isoften used conventionally as a lower soft magnetic film, even if wherethe vertical magnetic anisotropic energy Ku and the coercive force Hc inthe direction vertical to the film surface are much greater than thoseof conventional CoCr-based vertical magnetization films (e.g., Ku isabout 5×10⁶ [erg/cc] and Hc is about 3 [kOe]), as in the case of thematerial used in the present embodiment. Accordingly, it is possible toobtain a novel vertical two-layer medium which enables thinning of thelower soft magnetic film and easier process of manufacturing a medium.

From the results of the above first to ninth embodiments, it is apparentthat the same advantages as obtained in the first to ninth embodimentscan be obtained regardless of the material of the vertical magnetizationfilm, if the vertical magnetic anisotropic energy of the verticalmagnetization film falls within the range of 1×10⁷ [erg/cc]≦Ku≦7×10⁸[erg/cc] and if the coercive force in the direction vertical to the filmsurface of the vertical magnetization film falls within the range of 5[kOe]≦Hc≦10 [kOe].

Although embodiments of the present invention have been described aboveon the basis of the drawings, specific structures of the presentinvention were not limited to those described in the above embodimentsbut may be variously modified without deviating from the subject of thepresent invention.

As has been described above, according to the present invention, avertical magnetic recording medium was composed of layering a lower softmagnetic film and a vertical magnetization film on a substrate made of anon-magnetic material. Here, the lower soft magnetic film is arranged tosatisfy a relationship of μ·δ_(b)≧=1000 where μ is the magneticpermeability of the lower soft magnetic film and δ_(b) is the filmthickness thereof. Therefore, even if FePt alloy or RCo alloy (whereR=Y, Ce, Sm, La, Pr) as a vertical magnetization film has much greatervertical magnetic anisotropic energy Ku and a much greater coerciveforce Hc in the direction vertical to the film surface than those of aCoCr-based vertical magnetization film which is often usedconventionally and generally, the lower soft magnetic film can be morethinned than in the case of using a Ni_(21.5)Fe_(78.5) film which isoften used as the lower soft magnetic film. Accordingly, it is possibleto realize a easy process for preparing a medium and to obtain a novelvertical two-layer medium.

What is claimed is:
 1. A vertical magnetic recording medium comprising:a soft magnetic film formed on a substrate; and a vertical magnetizationfilm formed on said soft magnetic film, wherein μ·δb≧1000 where μ is apermeability of said soft magnetic film, and δb is a film thickness ofsaid soft magnetic film, and wherein vertical magnetic anisotropy energyKu of said vertical magnetization film is 1×10⁷≦Ku≦7×10⁸.
 2. A verticalmagnetic recording medium comprising: a soft magnetic film formed on asubstrate; and a vertical magnetization film formed on said softmagnetic film, wherein μ·δb≧1000 where μ is a permeability of said softmagnetic film, and δb is a film thickness of said soft magnetic film,and wherein coercive force Hc of said vertical magnetization film in thevertical direction to a surface of said vertical magnetization film is5≦Hc≦10.
 3. A vertical magnetic recording medium comprising: a softmagnetic film formed on a substrate; and a vertical magnetization filmformed on said soft magnetic film, wherein μ·δb≧1000 where μ is apermeability of said soft magnetic film, and δb is a film thickness ofsaid soft magnetic film, and wherein said vertical magnetization filmcomprises RCo alloy, where R is one or more selected from the groupconsisting of Y, Ce, Sm, La and Pr.
 4. The vertical magnetic recordingmedium according to claim 3, wherein said vertical magnetization filmcomprises RCo₅ alloy, where R is one or more selected from the groupconsisting of Y, Ce and Sm.
 5. The vertical magnetic recording mediumaccording to claim 3, wherein said vertical magnetization film comprisesR₂Co₁₇ alloy, where R is one or more selected from the group consistingof Y, Ce, Sm, La and Pr.
 6. A vertical magnetic recording mediumcomprising: a soft magnetic film formed on a substrate; and a verticalmagnetization film formed on said soft magnetic film, wherein μ·δb≧1000,where μ is a permeability of said soft magnetic film, and δb is a filmthickness of said soft magnetic film, wherein said soft magnetic filmcomprises CoNiFe alloy, and wherein said soft magnetic film comprises62at %Co-12at %Ni-26at %Fe alloy.
 7. A vertical magnetic recordingmedium comprising: a soft magnetic film formed on a substrate; and avertical magnetization film formed on said soft magnetic film, whereinμ·δb≧1000 where μ is a permeability of said soft magnetic film, and δbis a film thickness of said soft magnetic film, said permeability μ ofsaid soft magnetic film is 5≦μ≦200, said film thickness δb of said softmagnetic film is equal to or less than 500 nm, and wherein said verticalmagnetization film comprises RCo alloy, where R is one or more selectedfrom the group consisting of Y, Ce, Sm, La and Pr.
 8. A verticalmagnetic recording medium comprising: a soft magnetic film formed on asubstrate; and a vertical magnetization film formed on said softmagnetic film, wherein μ·δb≧1000 where μ is a permeability of said softmagnetic film, and δb is a film thickness of said soft magnetic film,said permeability μ of said soft magnetic film is 5≦μ≦200, said filmthickness δb of said soft magnetic film is equal to or less than 500 nm,and wherein vertical magnetic anisotropy energy Ku of said verticalmagnetization film is 1×10⁷≦Ku≦7×10⁸.
 9. A vertical magnetic recordingmedium comprising: a soft magnetic film formed on a substrate; and avertical magnetization film formed on said soft magnetic film, whereinμ·δb≧1000 where μ is a permeability of said soft magnetic film, and δbis a film thickness of said soft magnetic film, said permeability μ ofsaid soft magnetic film is 5≦μ≦200, said film thickness δb of said softmagnetic film is equal to or less than 500 nm, and wherein coerciveforce Hc of said vertical magnetization film in the vertical directionto a surface of said vertical magnetization film is 5≦Hc≦10.